Region of interest (ROI) is zoomed in reconstruction. As ROI is zoomed in an image, the details of the image experience poor quality. Particularly, the challenge becomes apparent for a zoomed image that has been reconstructed using an iterative reconstruction (IR) technique. In general, a reprojection step in IR requires knowledge of the entire object attenuating the x-ray beam. In contrast, analytic filtered back projection (FBP) generally reconstructs an image within the zoomed ROI without the need of the full field of view (FOV) reconstruction, provided that projection data is not truncated.
To overcome the above described challenge in IR, the following approaches have been suggested. Although one prior art technique removed a part of the projection data that corresponds to the outside of ROI in the image volume, the image quality was degraded due to the lacking features in the exterior areas of ROI. Another prior art technique utilized two volume grids including a coarse grid and a fine grid. Unfortunately, the prior art technique was computationally ineffective, and the coarse grid also limited spatial resolution of the fine grid.
In view of the above and other prior art techniques, a multi-scale reconstruction is still desired using not only an iterative reconstruction technique but also an analytic reconstruction technique.